The present invention relates to post-mix beverage dispenser valves such as for soft drinks and juices, and in particular to the use of a fluidic oscillator as a volumetric flowmeter and a piezo electric film transducer as a flow sensor in such a valve.
Traditional post-mix beverage dispensing valves include separate water (carbonated or still) and syrup (or concentrate) conduits and separate flow regulators located therein upstream of electrically or mechanically actuated on/off control valves. Each flow regulator utilizes a spring-loaded cylindrical piston as a combination of force and valving element; the piston is able to reciprocate freely within the cylinder and respond to the pressure difference at the two ends of the cylinder, as shown, for example, in U.S. Pat. Nos. 4,230,147; 3,422,842; and 2,984,261. The function of the piston and cylinder assembly is to maintain a constant pressure differential across the metering orifice machined directly in the face of the cylindrical piston, and to thus provide a constant flow regardless of the fluid pressure changes at the dispensing valve inlets. The flow regulator components operate at low force levels and operation at low force levels has a drawback of fostering hysteresis because of contaminants interposed between moving parts, and close fit between the parts themselves. Furthermore, it has been experienced that free pistons sometimes tend to stick in the regulator cylinder without regard to fit and finishing of the piston and the cylinder.
More recently, improvements in such valves to control the ratio of water to syrup have included the use of flow meters and control elements, as shown, for example, in U.S. Pat. No. 4,487,333. The known flow meters are relatively expensive and include moving parts.